CVE-2026-90110 inetpeer: randomize RB-tree node comparison using SipHash
Off-path attackers can bypass ICMP rate limits and infer open UDP ports by predicting Linux kernel inetpeer tree topology.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-90110?
CVE-2026-90110 is a critical vulnerability in Linux, published on 17 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
inetpeer: randomize RB-tree node comparison using SipHash
The inetpeer rate limiting system stores peer entries in a Red-Black tree keyed deterministically on the remote IP address. Because tree lookups walk the RB-tree using standard lexicographical comparisons (inetpeer_addr_cmp), an off-path adversary can predict the exact topology of the tree and the sequence of nodes traversed during lookups (the gc_stack candidate list).
By combining deterministic tree traversal with aggressive garbage collection (triggered when tree size exceeds inet_peer_threshold), an attacker can selectively force the eviction of targeted inet_peer nodes. When an evicted node is subsequently re-created upon receiving a new packet, its rate-limiting token bucket (rate_tokens, rate_last) is reset to full capacity. This creates a side-channel primitive allowing off-path attackers to bypass IP-keyed ICMP rate limits and infer open UDP ports (similar to SAD DNS style attacks).
Mitigate this by randomizing the RB-tree node comparison logic using SipHash with a secret key (inetpeer_hash_key) initialized via net_get_random_once(). Nodes are ordered in the tree by SipHash(addr, key) rather than raw IP addresses. Because the secret key is unknown to external entities, the tree layout and lookup traversal paths are unpredictable to off-path adversaries, breaking the deterministic eviction gadget.
Cache the computed 64-bit SipHash (hash) in struct inet_peer and compute the target hash (dhash) once at the beginning of inet_getpeer() to avoid recomputing SipHash at every step of the RB-tree walk.
Which versions are affected by CVE-2026-90110?
How do I fix CVE-2026-90110?
Apply the vendor's patch.
Is CVE-2026-90110 being exploited?
There is no known exploitation of CVE-2026-90110 in the wild and no public exploit code.
Sources
Also known as AZL-103026, BELL-CVE-2026-90110, DEBIAN-CVE-2026-90110, GHSA-cf89-f375-p3pc, UBUNTU-CVE-2026-90110.